Polarization-independent narrow-band optical filters with suspended subwavelength silica grating in the infrared region

We numerically demonstrate that a properly designed guided mode resonance filter (GMRF) with suspended silica (SiO2) subwavelength grating (SSG) can exhibit non-polarizing resonant filtering effect under normal incidence. By choosing appropriate parameters, including the incident wavelength, the grating period, the grating thickness, and the fill factor, the same resonance wavelengths for both transverse electric (TE) and transverse magnetic (TM) polarizations can be achieved. Results show that high reflection (more than 99.9%) can be obtained at the resonance wavelength (1.55 μm), and the full-width at half maximums (FWHMs) of TE- and TM-polarized light are only 1.0 × 10−2 μm and 1.4 × 10−3 μm, respectively. The reflectance peak splits into two branches when the incident light deviates from normal incidence. It is expected that the designed SSG should have applications in optical telecommunication systems or wavelength division multiplexing systems with an arbitrary state of polarization.